The plots of the estimated Rt over the most recent weeks show that the Rt appears to be following a declining trend in the absence of any further major relaxation of pandemic mitigation measures. Of all the regions, the NE had the highest recent peak in Rt of 1.53 (CrI 1.32–1.75) with a subsequent fall to 1.20 (1.00–1.41). This downward trend in R from the peak is still largely driven by the indices of mobility (from Google and school attendance).
From the end of March onwards, the incidence of deaths fell more sharply than predicted by the model, though both data and predicted trends are now showing a gradual rise over recent weeks. This does suggest that the ONS estimates and the data on deaths are giving conflicting signals. While this lack of fit has been reduced this week, further model development is ongoing to rectify this discrepancy.
Plots of the IFR over time show that from the end of January we estimate a decreasing IFR in all adult age groups, but most steeply in the older ages. This drop indicates the benefits of immunisation against death over and above the benefits against infection. Specifically, there is an estimated fall to a still-high 2.2% (1.9%–2.6%) in the over-75s and 0.10% (0.09%–0.11%) overall. The overall impact of the immunisation programme can be seen more clearly in the `All Ages’ plot, where the precipitous decline in IFR since late January is a product of this efficacy against death but also of the increasing proportion of infections in young people; older age groups are immunised and become more protected against infection. The impact of the immunisation in the 25–44 age-group is beginning to become apparent with a fall after an initial plateau.
For context, alongside the data used here, other indicators (e.g. hospital admissions, reported new positive tests) are suggesting a resurgent epidemic, largely due to the increasing dominance and spread of the Delta strain. Prevalence of infection, as estimated by the ONS Coronavirus Infections Survey, is close to 0.6% in England, though there is considerable regional heterogeneity. Again, as we move towards the 19th July and the complete lifting of social-distancing measures with an Rt dropping towards 1, there is the potential for the epidemic to display a range of qualitative behaviours over the coming period. The next few weeks will be crucial.
Real-time tracking of an epidemic, as data accumulate over time, is an essential component of a public health response to a new outbreak. A team of statistical modellers at the MRC Biostatistics Unit (BSU), University of Cambridge, are working to provide regular now-casts and forecasts of COVID-19 infections and deaths. This information feeds directly to the SAGE sub-group, Scientific Pandemic Influenza sub-group on Modelling (SPI-M), and to regional Public Health England (PHE) teams.
We fit a transmission model (Birrell et al. 2020) to a number of data sources (see ‘Data Sources’), to reconstruct the number of new COVID-19 infections over time in different age groups and NHS regions, estimate a measure of ongoing transmission and predict the number of new COVID-19 deaths.
We use:
Data are stratified into eight age groups: <1, 1-4, 5-14, 15-24, 25-44, 45-64, 65-74, 75+, and the NHS England regions (North East and Yorkshire, North West, Midlands, East of England, London, South East, South West).
Value of \(R_t\), the average number of secondary infections due to a typical infection today.
The percentage of a given group that has been infected.
NB: negative growth rates are rates of decline. Values are daily changes.
| Region | Median | 95% CrI (lower) | 95% CrI (upper) |
|---|---|---|---|
| England | 0.02 | 0.01 | 0.03 |
| East of England | 0.01 | -0.02 | 0.04 |
| East Midlands | 0.01 | -0.02 | 0.04 |
| London | 0.02 | -0.01 | 0.05 |
| North East | 0.03 | 0.00 | 0.05 |
| North West | 0.01 | -0.02 | 0.04 |
| South East | 0.02 | -0.01 | 0.04 |
| South West | 0.01 | -0.03 | 0.04 |
| West Midlands | 0.02 | -0.01 | 0.05 |
| Yorkshire and The Humber | 0.02 | -0.02 | 0.04 |
Halving times in days, if a region shows growth than value will be NA.
| Region | Median | 95% CrI (lower) | 95% CrI (upper) |
|---|---|---|---|
| England | NA | NA | NA |
| East of England | NA | 35.65 | NA |
| East Midlands | NA | 31.07 | NA |
| London | NA | 101.42 | NA |
| North East | NA | NA | NA |
| North West | NA | 40.83 | NA |
| South East | NA | 52.71 | NA |
| South West | NA | 25.18 | NA |
| West Midlands | NA | 95.27 | NA |
| Yorkshire and The Humber | NA | 42.80 | NA |
Doubling times in days, if a region shows decline then the value will be NA.
| Region | Median | 95% CrI (lower) | 95% CrI (upper) |
|---|---|---|---|
| England | 30.81 | 20.72 | 62.63 |
| East of England | 55.07 | 15.95 | NA |
| East Midlands | 61.41 | 16.46 | NA |
| London | 28.59 | 13.60 | NA |
| North East | 27.72 | 14.76 | 7047.29 |
| North West | 57.83 | 18.08 | NA |
| South East | 43.40 | 16.31 | NA |
| South West | 94.74 | 17.58 | NA |
| West Midlands | 32.73 | 13.87 | NA |
| Yorkshire and The Humber | 45.91 | 15.59 | NA |
NB: negative growth rates are rates of decline. Values are daily changes.
| Region | Median | 95% CrI (lower) | 95% CrI (upper) |
|---|---|---|---|
| England | 0.03 | 0.02 | 0.04 |
| East of England | 0.02 | -0.01 | 0.05 |
| East Midlands | 0.02 | -0.01 | 0.05 |
| London | 0.03 | 0.00 | 0.06 |
| North East | 0.04 | 0.02 | 0.07 |
| North West | 0.03 | 0.00 | 0.05 |
| South East | 0.02 | 0.00 | 0.05 |
| South West | 0.02 | -0.01 | 0.05 |
| West Midlands | 0.03 | 0.00 | 0.06 |
| Yorkshire and The Humber | 0.02 | 0.00 | 0.05 |
Halving times in days, if a region shows growth than value will be NA.
| Region | Median | 95% CrI (lower) | 95% CrI (upper) |
|---|---|---|---|
| England | NA | NA | NA |
| East of England | NA | 71.80 | NA |
| East Midlands | NA | 99.02 | NA |
| London | NA | NA | NA |
| North East | NA | NA | NA |
| North West | NA | NA | NA |
| South East | NA | 227.22 | NA |
| South West | NA | 67.98 | NA |
| West Midlands | NA | NA | NA |
| Yorkshire and The Humber | NA | 248.67 | NA |
Doubling times in days, if a region shows decline then the value will be NA.
| Region | Median | 95% CrI (lower) | 95% CrI (upper) |
|---|---|---|---|
| England | 24.71 | 17.85 | 37.91 |
| East of England | 39.08 | 14.62 | NA |
| East Midlands | 36.01 | 14.24 | NA |
| London | 23.35 | 11.86 | 158.73 |
| North East | 16.28 | 9.84 | 41.14 |
| North West | 27.13 | 13.47 | 658.51 |
| South East | 32.80 | 14.35 | NA |
| South West | 46.16 | 15.01 | NA |
| West Midlands | 24.23 | 11.99 | 253.01 |
| Yorkshire and The Humber | 31.74 | 13.71 | NA |
The shaded areas show periods of national lockdown, the green lines the dates (once confirmed) of the steps in the roadmap in the UK Governement’s COVID-19 Response – Spring 2021, and the red line shows the date these results were produced (12 Jul).
The figure below shows the probability that \(R_t\) is greater than 1 (ie: the number of infections is growing) in each region over time. Clicking the regions in the legend allows lines to be added or removed from the figure.
Copyright © MRC Biostatistics Unit, University of Cambridge